on 2015/12/15 23:43, Petr Mladek wrote: > On Mon 2015-12-14 20:49:35, Li Bin wrote: >> This patchset depends on the on-going gcc feature "-fprolog-pad=N", >> which will generate a pad of N nops at the beginning of each function. >> >> Livepatch on arm64 can using the feature (that always placing one nop >> at the beginning of the function). And when enable/disable func patching, >> just modify the pad code to nop or branch. And that NOP and B instruction >> are both safe instructions on arm64 which called "concurrent modification >> and execution of instructions", that can be executed by one thread of >> execution as they are being modified by another thread of execution without >> requiring explicit synchronization. >> >> And this method will improve performance significantly compared with the >> method based on ftrace, especially for the critical function being frequently >> called. > It sounds like a great feature for ftrace. If the new prologue is usable > for LivePatching, it should be usable to call the ftrace handler as > well. If you teach ftrace to use the new prologue, you will not need > all these crazy arch-specific hacks for LivePatching. Then both ftrace > and livepatch will benefit from the feature. > > I suggest to read the ftrace documentation in Documentation/trace/, > especially ftrace-design.txt. I have never ported ftrace to a new > architecture. I guess that you need to teach scripts/recordmcount.c > to find the new location. Also you might need to update > arch/arm/kernel/ftrace.c. Also please make sure that ftrace > supports DYNAMIC_FTRACE_WITH_REGS on Arm. Hi Petr, I had posted one method for livepatch implementaion on arm64 based on ftrace with DYNAMIC_FTRACE_WITH_REGS. https://lwn.net/Articles/646317/ This requires GCC changes to support it, and I propose a method that implement -mfentry feature which following some other arch such as x86/mips/s390 etc. This method is architecture-specific, and Maxim Kuvyrkov propose a new method for gcc that implement a target-independent option -fprolog-pad=N, which will generate a pad of N nops at the beginning of each function. https://gcc.gnu.org/ml/gcc/2015-05/msg00267.html And based on this, DYNAMIC_FTRACE_WITH_REGS feature can be implemented as mentioned in: http://lists.infradead.org/pipermail/linux-arm-kernel/2015-November/386815.html And in this patchset, I only concern the performance for livepatch on arm64, and I hope this also can be resolved by improving ftrace, and thanks to Steve that he pointed that he is working on a way to make ftrace a bit better for livepatch. Thanks, Li Bin > It is harder but the right way to go. Your current patch set > looks like a hack. > > Best Regards, > Petr > > . > -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
